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Article: Rhenium-osmium isotope and platinum-group elements in the Xinjie layered intrusion, SW China: Implications for source mantle composition, mantle evolution, PGE fractionation and mineralization

TitleRhenium-osmium isotope and platinum-group elements in the Xinjie layered intrusion, SW China: Implications for source mantle composition, mantle evolution, PGE fractionation and mineralization
Authors
KeywordsDissolution
Emplacement
Fractionation
Igneous intrusion
Isotopic analysis
Issue Date2011
PublisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/gca
Citation
Geochimica Et Cosmochimica Acta, 2011, v. 75 n. 6, p. 1621-1641 How to Cite?
AbstractThe Xinjie mafic-ultramafic layered intrusion in the Emeishan large igneous province (ELIP) hosts Cu-Ni-platinum group element (PGE) sulfide ore layers within the lower part and Fe-Ti-V oxide-bearing horizons within the middle part. The major magmatic Cu-Ni-PGE sulfide ores and spatially associated cumulate rocks are examined for their PGE contents and Re-Os isotopic systematics. The samples yielded a Re-Os isochron with an age of 262±27Ma and an initial 187Os/ 188Os of 0.12460±0.00011 (γ Os(t)=-0.5±0.1). The age is in good agreement with the previously reported U-Pb zircon age, indicating that the Re-Os system remained closed for most samples since the intrusion emplacement. They have near-chondritic γ Os(t) values ranging from -0.7 to -0.2, similar to those of the Lijiang picrites and Song Da komatiites. Exceptionally, two samples from the roof zone and one from upper sequence exhibit radiogenic γ Os(t) values (+0.6 to +8.6), showing minor contamination by the overlying Emeishan basalts.The PGE-rich ores contain relatively high PGE and small amounts of sulfides (generally less than 2%) and the abundance of Cu and PGE correlate well with S, implying that the distribution of these elements is controlled by the segregation and accumulation of a sulfide liquid. Some ore samples are poor in S (mostly <800ppm), which may due to late-stage S loss caused by the dissolution of FeS from pre-existing sulfides through their interaction with sulfide-unsaturated flowing magma. The combined study shows that the Xinjie intrusion may be derived from ferropicritic magmas. The sharp reversals in Mg#, Cr/FeO T and Cr/TiO 2 ratios immediately below Units 2-4, together with high Cu/Zr ratios decreasing from each PGE ore layer within these cyclic units, are consistent with multiple magma replenishment episodes. The sulfides in the cumulate rocks show little evidence of PGE depletion with height and thus appear to have segregated from successive inputs of fertile magma. This suggests that the Xinjie intrusion crystallized from in an open magma system, e.g., a magma conduit. The compositions of the disseminated sulfides in most samples can be modeled by applying an R factor (silicate-sulfide mass ratio) of between 1000 and 8000, indicating the segregation of only small amounts of sulfide liquid in the parental ferropicritic magmas. Thus, continuous mixing between primitive ferropicritic magma and differentiated resident magma could lead to crystallization of chromite, Cr-bearing magnetite and subsequently abundant Fe-Ti oxides, thereby the segregation of PGE-rich Cu-sulfide.When considered in the light of previous studies on plume-derived komatiites and picrites worldwide, the close-to-chondritic Os isotopic composition for most Xinjie samples, Lijiang picrites and Song Da komatiites suggest that the ferropicritic magma in the ELIP were generated from a plume. This comprised recycled Neoproterozic oceanic lithosphere, including depleted peridotite mantle embedded with geochemically enriched domains. The ascending magmas thereafter interacted with minor (possibly <10%) subducted/altered oceanic crust. This comparison suggests that the komatiitic melts in the ELIP originated from a greater-than normal degree of melting of incompatible trace element depleted, refractory mantle components in the plume source. © 2011 Elsevier Ltd.
Persistent Identifierhttp://hdl.handle.net/10722/139218
ISSN
2015 Impact Factor: 4.315
2015 SCImago Journal Rankings: 3.016
ISI Accession Number ID
Funding AgencyGrant Number
National Basic Research Program of China2007CB411401
"CAS Hundred Talents" Foundation of the Chinese Academy of Sciences
National Natural Science Foundation of China40473025
40873028
Funding Information:

The authors would like to thank the assistance of Mr. Yi Zhang during the field trip, and Mr. De-Ming Mo in major element wet chemical analysis. This paper benefited greatly from thorough and constructive reviews by I.S. Puchtel and H.J. Stein, especially in the plotting and interpreting of the Re Os data, and from very detailed and thoughtful comments by C. Li. and A.J. Naldrett is thanked for proofreading the manuscript. Editorial handling by E.M. Ripley is acknowledged. This study was jointly supported by the National Basic Research Program of China (2007CB411401), the "CAS Hundred Talents" Foundation of the Chinese Academy of Sciences to HZ, and the National Natural Science Foundation of China (40473025; 40873028).

References

 

DC FieldValueLanguage
dc.contributor.authorZhong, Hen_HK
dc.contributor.authorQi, Len_HK
dc.contributor.authorHu, RZen_HK
dc.contributor.authorZhou, MFen_HK
dc.contributor.authorGou, TZen_HK
dc.contributor.authorZhu, WGen_HK
dc.contributor.authorLiu, BGen_HK
dc.contributor.authorChu, ZYen_HK
dc.date.accessioned2011-09-23T05:47:13Z-
dc.date.available2011-09-23T05:47:13Z-
dc.date.issued2011en_HK
dc.identifier.citationGeochimica Et Cosmochimica Acta, 2011, v. 75 n. 6, p. 1621-1641en_HK
dc.identifier.issn0016-7037en_HK
dc.identifier.urihttp://hdl.handle.net/10722/139218-
dc.description.abstractThe Xinjie mafic-ultramafic layered intrusion in the Emeishan large igneous province (ELIP) hosts Cu-Ni-platinum group element (PGE) sulfide ore layers within the lower part and Fe-Ti-V oxide-bearing horizons within the middle part. The major magmatic Cu-Ni-PGE sulfide ores and spatially associated cumulate rocks are examined for their PGE contents and Re-Os isotopic systematics. The samples yielded a Re-Os isochron with an age of 262±27Ma and an initial 187Os/ 188Os of 0.12460±0.00011 (γ Os(t)=-0.5±0.1). The age is in good agreement with the previously reported U-Pb zircon age, indicating that the Re-Os system remained closed for most samples since the intrusion emplacement. They have near-chondritic γ Os(t) values ranging from -0.7 to -0.2, similar to those of the Lijiang picrites and Song Da komatiites. Exceptionally, two samples from the roof zone and one from upper sequence exhibit radiogenic γ Os(t) values (+0.6 to +8.6), showing minor contamination by the overlying Emeishan basalts.The PGE-rich ores contain relatively high PGE and small amounts of sulfides (generally less than 2%) and the abundance of Cu and PGE correlate well with S, implying that the distribution of these elements is controlled by the segregation and accumulation of a sulfide liquid. Some ore samples are poor in S (mostly <800ppm), which may due to late-stage S loss caused by the dissolution of FeS from pre-existing sulfides through their interaction with sulfide-unsaturated flowing magma. The combined study shows that the Xinjie intrusion may be derived from ferropicritic magmas. The sharp reversals in Mg#, Cr/FeO T and Cr/TiO 2 ratios immediately below Units 2-4, together with high Cu/Zr ratios decreasing from each PGE ore layer within these cyclic units, are consistent with multiple magma replenishment episodes. The sulfides in the cumulate rocks show little evidence of PGE depletion with height and thus appear to have segregated from successive inputs of fertile magma. This suggests that the Xinjie intrusion crystallized from in an open magma system, e.g., a magma conduit. The compositions of the disseminated sulfides in most samples can be modeled by applying an R factor (silicate-sulfide mass ratio) of between 1000 and 8000, indicating the segregation of only small amounts of sulfide liquid in the parental ferropicritic magmas. Thus, continuous mixing between primitive ferropicritic magma and differentiated resident magma could lead to crystallization of chromite, Cr-bearing magnetite and subsequently abundant Fe-Ti oxides, thereby the segregation of PGE-rich Cu-sulfide.When considered in the light of previous studies on plume-derived komatiites and picrites worldwide, the close-to-chondritic Os isotopic composition for most Xinjie samples, Lijiang picrites and Song Da komatiites suggest that the ferropicritic magma in the ELIP were generated from a plume. This comprised recycled Neoproterozic oceanic lithosphere, including depleted peridotite mantle embedded with geochemically enriched domains. The ascending magmas thereafter interacted with minor (possibly <10%) subducted/altered oceanic crust. This comparison suggests that the komatiitic melts in the ELIP originated from a greater-than normal degree of melting of incompatible trace element depleted, refractory mantle components in the plume source. © 2011 Elsevier Ltd.en_HK
dc.languageengen_US
dc.publisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/gcaen_HK
dc.relation.ispartofGeochimica et Cosmochimica Actaen_HK
dc.subjectDissolution-
dc.subjectEmplacement-
dc.subjectFractionation-
dc.subjectIgneous intrusion-
dc.subjectIsotopic analysis-
dc.titleRhenium-osmium isotope and platinum-group elements in the Xinjie layered intrusion, SW China: Implications for source mantle composition, mantle evolution, PGE fractionation and mineralizationen_HK
dc.typeArticleen_HK
dc.identifier.emailZhou, MF:mfzhou@hkucc.hku.hken_HK
dc.identifier.authorityZhou, MF=rp00844en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1016/j.gca.2011.01.009en_HK
dc.identifier.scopuseid_2-s2.0-79951515280en_HK
dc.identifier.hkuros195325en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-79951515280&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume75en_HK
dc.identifier.issue6en_HK
dc.identifier.spage1621en_HK
dc.identifier.epage1641en_HK
dc.identifier.isiWOS:000287682500013-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridZhong, H=35785435900en_HK
dc.identifier.scopusauthoridQi, L=7202149924en_HK
dc.identifier.scopusauthoridHu, RZ=7202640800en_HK
dc.identifier.scopusauthoridZhou, MF=7403506005en_HK
dc.identifier.scopusauthoridGou, TZ=26421205300en_HK
dc.identifier.scopusauthoridZhu, WG=35785330800en_HK
dc.identifier.scopusauthoridLiu, BG=49161225100en_HK
dc.identifier.scopusauthoridChu, ZY=7101763057en_HK
dc.identifier.citeulike8668973-

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